Architectural compositions such as paints and stains include a film-forming continuous phase component that may be aqueous or non-aqueous and that contains a polymer as a solute or as a colloidal dispersion. Opacifying pigments or pigments are particulate compounds dispersed in a paint binder to provide hiding power and color to paints and coatings. Pigments also improve the durability and weathering properties of paints, provide opacity and special effects, e.g., flip, sparkle, and modify flow and application properties. Dry pigments are dispersed in water and dispersants to form a grind, i.e., suspended in an aqueous solution. The grind is then added to aqueous a latex composition to form a paint or added in a colorant liquid composition. Heavy pigment particles are separated from one another and are distributed evenly throughout paint compositions as a colloidal suspension. Otherwise, a variety of defects can occur including color shift, flooding and floating, settling and loss of gloss. Pigments that have no charges on them and are not coated need surfactants or dispersants for better distribution.
After applying a paint or coating to a substrate and forming a film on the substrate, pigments in the paint or coating absorb and scatter light to prevent light from passing through the film to layers below on the substrate and back to the eye of an observer. The hiding power or opacifying power of paint is expressed by the number of square meters covered by 1 liter of paint to produce complete hiding. In addition, the hiding power of a pigment is expressed as the number of square meters covered by a kilogram of pigment dispersed in a paint such that when applied over previously applied paint layers, the pigment hides the color of any previous layer.
Typical opacifying pigments include titanium dioxide (TiO2), which has hiding power due to its high refractive indices and optimum particle size for maximum hiding power. For example, rutile titanium dioxide white has a particle diameter of 200 nm-300 nm. The distribution or arrangement of titanium dioxide particles in paint, however, affects the resulting hiding power. For example, titanium dioxide can be transparent when present in the form of large clusters of particles, and its hiding power is reduced significantly when agglomerated due to reduced light scattering efficiency. Conversely, good particle dispersion increases the hiding efficiency of titanium dioxide particles in paint. Additives such as dispersing agents and surfactants are used in paints to prevent titanium dioxide particles from agglomerating and to maximize the hiding power of the titanium dioxide particles in those paints.
Another consideration in the use of titanium dioxide as an opacifying pigment in paints is cost. Since titanium dioxide is an expensive component, cost savings are realized through the use of decreased amounts of titanium dioxide. Attempts to reduce the amount of titanium dioxide as a hiding or opacifying pigment in paint compositions are discussed in U.S. Pat. No. 5,385,960 to Emmons et al., U.S. Pat. No. 6,080,802 to Emmons et al., U.S. Patent Application Publication no. 2012/0058277 to Bohling et al., and U.S. Patent Application Publication no. 2012/0058278 to Bohling et al., and U.S. Pat. No. 7,960,026 to Koller et al.
These previous attempts only used monomers having the desired functionality for titanium dioxide particle attachment. Other additives generally found in paints and coatings include surfactants. Surfactants include both hydrophobic and hydrophilic ends and are typically added, for example, during the grind or letdown stages of paint formation in order to achieve the desired, dispersion of particles in the paint. International Patent Application no. PCT/US2013/039784 to Palmer et al., discloses the creation of latex particles that are manufactured in the presence of a reactive surfactant. The titanium dioxide particles are then added to this latex particle dispersion. These latex particles, however, have a low glass transition temperature and function as the binder or film-forming polymer in the resultant paint films. Particles with low glass transition temperatures do not provide as reliable a spacing among the titanium dioxide particles. Therefore, coating compositions are desired that provide for more reliable spacing among opacifying particles in order to reduce the amount of opacifying pigment required in the coating composition.